This study is an ethnosemantic analysis, the goal of which is to study the meanings of words in a language to gain insight into the worldview of its speakers. The study aims to investigate Thai surnames bestowed by King Rama VI in four aspects: 1) the criteria used in coining the surnames, 2) the patterns and the structures of the surnames, 3) the meanings of the surnames, 4) Thai values reflected in those meanings. The data used for analysis were 3,000 surnames randomly selected from over 6,000 surnames available in the Dictionary of Thai Surnames Bestowed by King Rama VI. The hypotheses of this study are that there are two criteria in coining the surnames: the background of the name owner and the linguistic criterion. There are several patterns of the surnames which can be generalized as a rule indicating that the first part is always the ancestors name. The meanings of the surnames reflect some values and some aspects of Thai culture, such as the societal preference for a male, Thai preference for working as a civil servant and Chinese preference for being merchants. The result shows that there are two criteria in coining a surname. One is based on the owner's background and another on the linguistic criteria: semantic and phonetic motivation. Concerning the patterns and the structures of the surnames, it is found that a surname is composed of two parts: 1.[head + (qualifier)] and 2.[at + place]. The second part is optional. Thus, the surnames have three patterns: 1. [ head + (qualifier)], 2.[at + place] and 3. [ head + (qualifier)] + [at + place]. The head in the first position is normally the name of an ancestor. Regarding the meanings of the surnames, the analysis of the part of surnames which is not derived from the background of the name owner indicates five most significant meanings; namely, happiness, prosperity, descent, personal characteristics, and wealth. These meanings reflect some significant values and some aspects of Thai culture: 1) aspiration in happiness, prosperity and wealth, 2) Thai preference for being civil servants and Chinese preference for being merchants and societal preference for a male to continue a line. 3) Also, the most admirable characteristics in a person are wisdom, mercy and sacrifice.